Bone and joint pain is relatively common among obese people, but until a recent study by University of Utah pain management researchers, being seriously overweight had not been definitively linked to pain sensitivity and other symptoms of the chronic and sometimes debilitating pain disorder fibromyalgia.

In a study with 215 people, however, Akiko Okifuji, Ph.D., professor of anesthesiology at the U of U School of Medicine, and colleagues at the U of U Pain Research and Management Center and Department of Anesthesiology found that obese fibromyalgia patients are more sensitive to pain, experience more physical disabilities, and don't sleep as well as those who have the syndrome but are not obese.

The findings don't establish a causal relationship between obesity and fibromyalgia syndrome, but they indicate a significant correlation between the two, according to Okifuji, who also holds the Scott M Smith MD Presidential Endowed Chair in Anesthesiology.

"Our research raises questions about the link between obesity and fibromyalgia," she says. "Carrying those extra pounds might contribute to maintaining or exacerbating pain symptoms or even preventing people from getting better."

Fibromyalgia syndrome is a chronic, bodywide pain disorder of the musculoskeletal system that affects joints, muscles, and soft tissue and often is accompanied by fatigue, mood, sleep, and memory issues. It's estimated that up to 5 percent of Americans, mostly women, have fibromyalgia. No underlying cause of the syndrome has been identified, but researchers believe it might be related to the way pain signals are processed in the brain. In many cases, symptoms build up for years, with no triggering event. However, for some people, symptoms begin after a physical trauma, infection, major psychological stress or surgery.Â

Participants underwent a full fibromyalgia evaluation, including a tender point (TP) examination - which gauges pain sensitivity when an examiner uses a thumb to press 18 specific body points - physical performance testing, and a home sleep assessment.

Obese participants experienced significantly higher TP pain sensitivity (average rating of 5.92) than those of normal weight (average rating of 5.02) or who were somewhat overweight (average rating of 4.98). The obese group was particularly more sensitive to pain in the lower body, including the areas in the hips and knees.

The obese patients also showed reduced flexibility in the lower body, measured while they were lying on their backs and doing a straight leg raise.

In a home sleep assessment, participants wore a wristwatch-like device that measured sleep parameters for a week. Data showed the obese patients got an average of 41 minutes less sleep a night, were more restless and had a greater duration of waking time during sleep.

Overall, the study shows that obesity complicates the clinical picture for fibromyalgia, according to Okifuji. "I hope researchers now can begin to identify the mechanisms of how obesity influences fibromyalgia syndrome."

Recent studies have shown that losing weight can alleviate symptoms of fibromyalgia. Okifuji and her colleagues suspect that the relationship between weight loss and symptom reduction is indirect and mediated by currently unknown factors. A psychologist by training, Okifuji counsels her fibromyalgia patients to undertake sensible physical activity to lose weight - a daunting task for those with chronic pain who are not used to much physical exertion.

"It's difficult to change your lifestyle even if you are healthy, let alone being overweight, sedentary, and fatigued," she says. "But shifting to a healthier lifestyle may be one way these patients can reduce their symptoms and improve their quality of life."

The study appeared in the December issue of The Journal of Pain. Perry G. Fine, M.D., U professor of anesthesiology and president-elect of the American Academy of Pain Medicine is senior author. Gary W. Donaldson, Ph.D., U professor of anesthesiology, and Lynn Barck, a physical therapist with University of Utah Health Care, are co-authors